Foxconn Industrial Internet, a subsidiary of the world's largest contract manufacturer Foxconn, announced plans to raise up to 27.1 billion yuan ($4.26 billion) in what will be mainland China's biggest IPO in almost three years.

The Foxconn unit, which is known as FII and makes electronic devices, cloud service equipment and industrial robots, is offering up to 1.97 billion shares at 13.77 yuan per share in Shanghai, according to a statement it filed to the stock exchange late on Tuesday.

With 10 percent of its enlarged capital offered in the initial public offering (IPO), Shenzhen-based FII would have a valuation of about $43 billion at listing. Bookbuilding for the IPO is on May 24.

The listing is widely seen as a step for Terry Gou's Foxconn, a major Apple Inc supplier formally known as Hon Hai Precision Industry Co, to wean itself off heavy reliance on manufacturing smartphones for the California-based iPhone maker and to diversify into new areas.

The IPO is also a reflection of Beijing's seriousness in luring tech giants onto mainland exchanges.

At about $43 billion, the unit's valuation would not be far behind parent company Foxconn's market capitalisation of about $49 billion.

The IPO's pricing represents 17 times FII's historical earnings, well below the valuation cap of 23 times favoured by Chinese regulators.

FII plans to sell 30 percent of its public share offering to a group of strategic investors in a rare move for mainland deals.

The strategic investors are not being called cornerstones - investors who accept a lock-up period in return for large allocation, which is a practice common in other Asian markets such as Hong Kong to bolster demand for large deals.

However, the group will function as such, with its investments tied up for between one and three years. In an additional unusual move, 70 percent of institutional investors' allocated shares will also be locked up for 12 months.

FII's IPO ranks as the fourth largest in the mainland over the past 10 years, outpaced only by China State Construction Engineering, which raised $7.3 billion in 2009; China Railway Construction, which sold shares worth $5.7 billion in 2008; and Guotai Junan Securities, which raised $4.8 billion in 2015.

Clients of FII include companies such as Amazon, Apple, Cisco, Dell, Huawei and Lenovo.